This invention generally relates to image sensing devices, and more particularly relates to correction circuits for image sensors.
Dark current nonuniformities are present in CCD and CMOS active pixel sensors. The dark current nonuniformities result from material impurities which are not uniformly distributed in the substrate. Some prior art solutions to the nonuniformities include substituting neighboring pixels and smoothing the amplitude by analog signal processing methods. Analog signal processing results in art effects and incorrect pixel correction.
Generally, and in one form of the invention, the method of compensating for nonuniformities in an image sensor includes: providing an image sensing device; measuring test pixel signals from the image sensing device during a test mode; determining which test pixel signals are greater than a fixed threshold level; and calculating nonuniformity coefficients for the pixels having test pixel signals greater than the fixed threshold level. The processing for correcting pixel nonuniformities is in the digital domain.